This invention relates to an electronic tissue stimulator. More specifically, the invention relates to an improved neuromodulation system for managing various diffuse and multi-focal neurological and/or motor disorders.
The concept of using electronic stimulation systems to control pain by nerve or muscle stimulation is well known. Spinal cord stimulation (SCS) is a technique that has been used for pain management since the 1960s. SCS systems feature a pulse generator, discussed further below, coupled to one or more percutaneous leads having a plurality of electrodes (systems may also use a paddle-type lead that requires insertion by laminectomy). The leads are positioned within a patient""s epidural space, parallel to the axis of the spinal cord. The leads"" electrodes are used to deliver a particularized electric field to a specific region of the spinal cord or surrounding tissue. Applying an electric field across one or more nerve bundles and/or nerve roots can produce paresthesia, or a subjective sensation of numbness, tingling or xe2x80x9cpins and needles,xe2x80x9d at the affected nerves"" dermatomes. This paresthesia, if properly directed and produced at the necessary levels, can xe2x80x9cmaskxe2x80x9d certain forms of chronic pain.
The focus, characteristics and intensity of the generated electric field are determined by the electrode configuration (i.e., the polarity, if any, assumed by each electrode) and the electric pulse waveform (collectively xe2x80x9cstimulation settingxe2x80x9d). The waveform properties include, at least, a stimulation frequency, a stimulation pulse width and phase information.
SCS systems are of two types. The most common system is a totally implanted pulse generator (IPG). An IPG consists of a surgically implanted, internally-powered pulse generator and, typically, a single multi-electrode lead. Once implanted, the IPG may be activated and controlled (programmed) by an outside telemetry source. The patient, being largely relieved of daily interaction with the system, uses a small magnet to both turn the system on and off and limitedly control the stimulation settings. The internalized power source limits the life of these systems to between two and four years. After the power source is expended, the patient is required to undergo replacement surgery to continue electrical stimulation.
The second type of SCS system is a radio frequency (RF) system. An RF system consists of a surgically implanted, passive receiver and a transmitter which is worn externally. The transmitter is connected to an antenna which is positioned, externally, over the site of the implanted receiver. In operation, the transmitter communicates, through an RF signal, to the implanted receiver. Just as with the IPG system, electrical stimulation is delivered via implanted leads. Differing from an IPG, however, RF systems typically posses greater power resources, thereby enabling RF systems to utilize multiple leads. An RF system, like the one described herein, is disclosed in U.S. Pat. No. 4,612,934, issued Sep. 23, 1986, to Borkan.
Although existing systems have proven effective, these systems provide only qualified relief to patients who experience multi-focal or complex pain. Current SCS systems can address, at a maximum, two distinct pain patternsxe2x80x94a xe2x80x9cpain patternxe2x80x9d being a dermatome, dermatome segment or series of dermatomes afflicted by pain. One current system features two percutaneous leads, wherein the user can elect to address up to two unilateral pain patterns or a single non-complex, non-migrating bilateral pain pattern.
xe2x80x9cUnilateral painxe2x80x9d is said to be that pain which is localized on one side of the patient""s body or the other. Unilateral pain is most efficiently addressed through a xe2x80x9cunilateral electrode array,xe2x80x9d or a lead which is positioned to one side or the other of the physiological midline of the spine, e.g., an electrode positioned to the left of the physiological midline typically addresses pain located on the left side of the patient""s body. Therefore, logically, xe2x80x9cbilateral painxe2x80x9d is that pain which affects both sides of the patient""s body, for example, lower back pain is often considered bilateral in nature. A bilateral electrode array generates an electric field to address bilateral pain. A bilateral electrode array may take two forms: (i) a single multi-electrode array positioned on or immediately about the physiological midline of the patient; or (ii) two parallel multi-electrode leads positioned to either side of the physiological midline, in which the leads produce a single electric field which transverses the spinal cord. As began above, the system of this example can be configured to address two unilateral pain patterns or a single bilateral pain pattern. The limitation inherent with this system is that a patient can experience only xe2x80x9ceither-orxe2x80x9d pain management. Therefore, the patient is restricted to the simplest form of xe2x80x9cmulti-focalxe2x80x9d stimulation applications.
For those patients whose pain does not conform to the non-yielding stricture of prior art systems, it would be desirable to provide an improved SCS system, whether an IPG or RF system, which could accommodate three or more stimulation settings to address diffuse, multi-focal pain, whether of a unilateral or bilateral nature or any combination thereof. A further desire would be to allow a patient, at will, to tailor a stimulation treatment from a group of programmed stimulation settings, wherein the patient may select: (i) a single stimulation setting, (ii) any number of stimulation settings from the programmed group, the selected settings being administered xe2x80x9csimultaneouslyxe2x80x9d, or (iii) xe2x80x9csimultaneousxe2x80x9d stimulation of all programmed stimulation settings. xe2x80x9cSimultaneousxe2x80x9d stimulation being a mode of operation wherein each selected stimulation setting is delivered to the patient, the patient receiving the cumulative effect of each stimulation setting, and not substantially perceiving the transition from one stimulation setting to another.
In addition to the use of this technology for pain management, some researchers believe that SCS may have beneficial application in obtaining relief from and/or controlling the physical effects of peripheral vascular disease (PVD), angina pectoris, and various motor disorders.
It is, therefore, an object of the invention to provide an improved SCS system, the improved system being capable of being programmed with three or more stimulation settings to generate a corresponding number of electrical stimulation pulses.
It is another object of the invention to provide an improved SCS system which allows a patient, at will, to tailor a stimulation treatment from a group of programmed stimulation settings, wherein the user may select: (i) a single stimulation setting, (ii) any number of stimulation settings from the programmed group, the selected settings being administered xe2x80x9csimultaneouslyxe2x80x9d, or (iii) xe2x80x9csimultaneousxe2x80x9d stimulation of all programmed stimulation settings.
These and other objects of the invention are obtained by providing a microcomputer controlled system. The improved system is capable of storing and delivering at least three stimulation settings, each stimulation setting potentially addressing a differing region of the patient""s body. As well, each stimulation, setting can produce, if the system possesses more than one multi-electrode catheter, electric fields characteristic of either a unilateral or bilateral electrode array.
For example, for an RF system, the transmitter may store a plurality of stimulation settings. Stimulation settings include data concerning, at least, an electrode configuration (the defined electric polarity of each electrode, if any), a stimulation amplitude, a stimulation frequency, a stimulation pulse width and signal phase information. The treatment information is encoded in the transmitter and impressed on an RF carrier signal which is broadcast through a transmission antenna to the system""s implanted receiver.
An RF transmitter embodying the present invention is configured to include three or more setting data registers. Each of these data registers can be programmed to store an independent stimulation setting. Each independent stimulation setting can potentially target distinct regions of the patient""s body to relieve pain or address other conditions such as motor disorders. Associated with each of the different stimulation settings is a stimulation amplitude. Independent amplitude registers store each of the amplitude values. Since each amplitude is associated with a stimulation setting, this embodiment includes an equal number of setting data registers and amplitude registers. Each of the setting data registers are connected to a setting select multiplexer which is used to select a particular stimulation setting to be broadcast by the transmitter. Similarly, an amplitude select multiplexer is used to select the amplitude information associated with the selected stimulation setting.
To control the stimulation setting and associated amplitude broadcast to the receiver, the transmitter includes a programmable setting time generator which is controlled by the microcomputer. The setting time generator generates a treatment interval which is sent to a programmable setting counter. The treatment interval is the interval that a particular stimulation setting is broadcast before the transmitter switches to the next stimulation setting. In the xe2x80x9csimultaneousxe2x80x9d operations mode, the treatment modality is set such that the patient cannot discern the switching between stimulation setting intervals, or pulses, and feels only the cumulative effect of all settings. The setting counter uses the treatment interval to control the select lines of the setting and amplitude multiplexers. The counter allows the setting counter to cycle through the desired stimulation settings substantially sequentially and ensures that all elected settings are broadcast.
The system further includes a clock to provide a signal at a continuous frequency. This frequency is altered by a frequency divider according to the microcomputer, in accordance with the selected stimulation setting, to produce the desired stimulation frequency. The stimulation frequency is sent to a pulse width modulator which modifies the stimulation frequency to add the selected pulse width. All of the treatment information is combined at an RF modulator which impresses the combined treatment information on an RF carrier for broadcasting to the receiver.